1. Field of the Invention
This invention relates to dust excluding devices, and particularly to improvements in a dust excluding device suitable for use in a linear scale type measuring instrument and including flexible shield members disposed at opposite sides of an opening formed in a hollow casing along a line of movement of a movable member and having the forward ends being brought into abutting contact with each other, and a neck adapted to locally push open the abutting contact portions of the shield members, for imparting a displacement of the movable member at the outside of the hollow casing to the interior of the hollow casing through the opening.
2. Description of the Prior Art
In general, in the case of measuring a value of movement between articles movable relative to each other such for example as a value of movement of a measuring element relative to its main body, a value of movement of a slider with respect to a column and the like by use of a measuring instrument for measuring a length and the like of an article, there have been known linear scale type measuring instruments, in each of which a linear scale is fixed at one side and a detector including an index scale is fixed at the other side, whereby a value of a relative displacement between the linear scale and the detector is photoelectrically read.
The linear scale type measuring instrument of the type described, for example, comprises: a hollow casing fixed on a bed of a machine tool; a linear scale housed in and fixed to the hollow casing; a slider movable along the linear scale and mounted thereon with an index scale provided thereon with graduation fringes disposed adjacent graduation fringes of the linear scale; a detector movable with a workpiece or a tool; and a connecting mechanism for imparting a displacement of the detector to the slider disposed in the hollow casing. In the linear scale type measuring instruments as described above, there has been used a dust excluding device, such for example as shown in FIG. 1, comprising: flexible shield members 14, 16 made of rubber for example, disposed at opposite sides of an opening 12a formed along a line of movement of a detector 10 being a movable member and having the forward ends 14a, 16a being brought into abutting contact with each other; and a neck 18 adapted to locally push open the abutting contact portions of the shield members 14, 16, for imparting a displacement of the movable member at the outside of the hollow casing 12 to the interior of the hollow casing 12 through the opening 12a. In addition, both the linear scale disposed along the opening 12a of the hollow casing 12 and the slider adapted to travel along the linear scale with a predetermined distance being held from the linear scale in accordance with a displacement of the detector 10 are housed in the hollow casing 12, whereby a displacement of the detector 10 is imparted to the slider through a cantilever spring or the like provided on the neck 18 at the inner side of the hollow casing 12. By use of the dust excluding device as described above, at the portion of the hollow casing 12 where the neck 18 is not present, a slidably guiding surface of the linear scale for the slider in the hollow casing 12 is covered by the shield members 14, 16, so that dust can be excluded from intruding onto the slidably guiding surface. However, heretofore, the end portion of the neck 18 in the moving directions thereof, which are inserted through the shield members 14, 16, have been each formed into a letter `V` shape vertically upstanding with respect to a shielding surface formed by the shield members 14, 16 as shown in FIG. 2, and consequently, when the detector 10 moves in a direction indicated by an arrow A, the shield members 14, 16 are pushed open to the opposite sides. In this case, gaps B are formed between the side edges of the shield members 14, 16, which have been in abutting contact with each other, forwardly and rearwardly of the neck 18, thereby permitting dust to intrude onto the slidably guiding surface through the gaps B. Furthermore, during the movement, the forward end portion of the neck 18 disposed at the head in the advancing direction of the neck 18 is adapted to push open the abutting contact portions of the shield members 14, 16 perpendicularly to the shielding surface constituted by the shield members 14, 16, thus presenting such disadvantages that high travelling resistance due to the friction of the neck 18 and the like.